A virus strain which can lead to severe respiratory infections, Enterovirus D68, has gripped the United States, with an outbreak of close to 600 cases, almost all in children, since August.

The death of a four-year-old boy in New Jersey last month has been linked directly to the virus.

At least four others who were infected have also died, but the US Centers for Disease Control and Prevention (CDC) said that it is unclear what role the virus played in their deaths.

Here are six things to know about the potentially fatal virus, also known as EV-D68:

1. Enterovirus D68 is one of more than 100 strains of non-polio enteroviruses, which often cause nothing more than a cold.

2. The virus typically causes flu-like symptoms such as fever, running nose, sneezing, cough and body aches. In some cases it can cause wheezing and breathing problems that may require hospitalisation.

3. Infants, children and teenagers are most at risk of falling ill from the virus, especially children with asthma. Adults in contact with the virus are more likely to experience mild or no symptoms.

4. The virus spreads when an infected person coughs, sneezes, or touches a surface that is touched by others.

5. There is no vaccine to prevent EV-D68. Frequent hand-washing and not coughing into one's hands are some precautions.

6. There is no specific treatment for people with respiratory illness caused by EV-D68. It can only be diagnosed with specific lab tests on specimens from a person's nose and throat.

Sources: AFP, huffingtonpost.com, cdc.gov, reuters.com